1. Field of the Invention
The present invention relates to a wet type friction member. More particularly, it relates to a wet type friction member, which is constituted by bonding a plurality of segments of a friction member (i.e., segmental friction units) on a core plate.
2. Description of the Related Art
A wet type friction member is generally used a lot in an automotive clutch disk, and so on. In this case, the wet type friction member is usually constituted by a ring-shaped core plate and friction units, which are bonded on a surface of the core plate in a ring-shaped manner. The surface bonded with the friction units makes a friction surface.
Since such a wet type friction member is used a lot in a clutch disk, and so forth, it is required to exhibit an appropriate friction coefficient and a less dragging torque. Moreover, the friction surface generates heat by friction, it is also needed to be good in terms of a heat resistance and a heat resistant longevity.
Accordingly, in order to secure the heat resistance for the wet type friction member, oil grooves have been disposed conventionally in the friction surface of the wet type friction member so that the heated friction surface, specifically, the friction units, which are bonded on the core plate, are cooled by an oil, which passes through the oil grooves. When the wet type friction member is used as a clutch disk, there arises a centrifugal force and the oil is flowed by the centrifugal force in the oil grooves from the inner peripheral side of the core plate to the outer peripheral side thereof, because the wet type friction member rotates about the axial center.
As a method for providing the oil grooves, a plurality of segmental friction units have been conventionally bonded on the core plate at intervals in a ring-shaped manner, and the resulting intervals have been utilized as the oil grooves. Namely, it is a method, in which the oil grooves, which connect the inner peripheral side of the core plate with the outer peripheral surface thereof, are demarcated and formed by the facing end surfaces of the neighboring segmental friction units. For example, as illustrated in FIG. 19, as such a wet type friction member, there has existed a wet type friction member, in which the facing end surfaces, demarcating and forming the oil groove, of the segmental friction units are linear so that the resulting oil grooves are also linear and the groove width of the oil grooves is substantially constant.
Although the wet type friction member, in which the oil grooves are linear and have a substantially constant groove width, is improved in terms of the cooling performance, compared with a conventional wet type friction member, which is not provided with the grooves. However, there is a problem in that the cooling performance is still insufficient.
Hence, a large variety of improvements have been developed on the shape of the oil grooves. For instance, in Japanese Unexamined Patent Publication (KOKAI) No. 10-318,308 and Japanese Unexamined Patent Publication (KOKAI) No. 11-141,570, there are disclosed oil grooves of various configurations. In these publications, there are disclosed various configurations for oil grooves, which connect the inner peripheral side of the core plate with the outer peripheral side thereof, oil grooves which are opened on the inner peripheral side of the core plate but are not opened on the outer peripheral side thereof, and so forth. However, these configurations do not necessarily result in the sufficient improvement on the cooling performance.
It is therefore an object of the present invention to provide a wet type friction member, which comprises segmental friction units having a good configuration in terms of the cooling performance, and which exhibits a superb heat resistance. In addition, it is another object of the present invention to provide a wet type friction member, which comprises segmental friction units, which have a configuration being capable of reducing a dragging torque.
Therefore, the inventors of the present invention have earnestly carried out the research and development on the wet type friction member. As a result, they have invented a novel wet type friction member, which is characterized in that it comprises: a core plate; a plurality of segmental friction units bonded on the core plate at intervals in a ring-shaped manner; oil grooves demarcated and formed by facing end surfaces of neighboring two pieces of the segmental friction units, and connecting an inner peripheral side of the core plate with an outer peripheral side thereof; at least one of the facing end surfaces of the segmental friction units having a cut-off portion, being cut off inwardly, at an inner peripheral side end of the facing end surfaces and/or an intermediate portion thereof; and the oil grooves being provided with a major-width portion of a wide groove width by the cut-off portion at an inner peripheral side opening of the oil grooves and/or an intermediate portion thereof.
Since the oil, which passes in the oil grooves, exhibits a cooling effect, the portions adjacent to the oil grooves exhibit a high cooling effect but the portions between the oil grooves, in which the oil does not flow, exhibit a low cooling effect. Accordingly, in the oil grooves, which are linear and which have a substantially constant groove width, the oil flows too smoothly to fully utilize the cooling effect of the passing oil.
Hence, in the wet type friction member according to the present invention, the facing end surfaces of the segmental friction units, which demarcate and form the oil grooves, are provided with the cut-off portion, which is cut off inwardly, at an inner peripheral side end of the facing end surfaces and/or an intermediate portion thereof. Accordingly, the facing end surfaces are made non-linear. By thus providing the cut-off portion, the present wet type friction member has the oil grooves, whose groove width is not constant, and the major-width portion of a wide groove width at an inner peripheral side end of the facing end surfaces and/or an intermediate portion thereof. To put it differently, the oil grooves have the major-width portion having a wide groove width, and a minor-width portion, which has a groove width narrower than that of the major-width portion.
When the oil grooves have the major-width portion and the minor-width portion by providing the facing end surfaces with the cut-off portion, which is cut off inwardly, the oil, which flows in the oil grooves from the inner peripheral side to the outer peripheral side, is dammed temporarily by a point where the groove width varies, for example, at a point where the oil grooves change from the major-width portion to the minor-width portion, a part of the oil overflows onto the surface of the segmental friction units, and consequently flows on the segmental friction units.
Therefore, the present wet type friction member can be improved in terms of the cooling effect and can be enhanced in terms of the heat resistance by thus supplying the oil over a wide area of the segmental friction units.
Moreover, in the idling, the oil, flowing in the oil grooves from the inner peripheral side to the outer peripheral side, is dammed at the point where the groove width changes, a part of the oil flows out onto the surface of the segmental friction units. However, according to the present invention, it is possible to suppress the present wet type friction member from contacting with a mating plate, and to reduce the dragging torque.
Thus, the present wet type friction member can be improved in terms of the cooling effect, and can be enhanced in terms of the heat resistance. Moreover, it can be suppressed from contacting with a mating member, and can exhibit a reduced dragging torque.